Climate researchers and policy makers have raised concerns that there are no current or planned means to independently verify a nation's self-reported greenhouse gas (GHG) emissions inventory with sufficient accuracy to verify compliance with emission limits in future treaties or provide agencies responsible for administrating future carbon markets the ability to detect underreporting and misleading accounting. Mistrust of nations' self-reports is becoming a stumbling block in efforts to agree on more stringent carbon-reduction targets. Poorer nations cannot afford extensive in situ monitoring networks. And some nations are reluctant to allow on-site inspection or disclose economic proxy data.
Existing atmospheric carbon dioxide (CO2) sampling stations are not able to monitor emissions from large local sources or verify national emission inventories. In fact, existing in situ sensors are purposefully sited away from fossil fuel emission sources in order to better monitor natural sources and sinks for research purposes. Deploying a sufficient number of additional in situ GHG sensors for monitoring national emissions, though physically possible, would be extremely costly and require on-site personnel for maintenance and operation. Also, in situ sensors are vulnerable to tampering and vandalism. Nor is a constellation of satellites with sensors capable of measuring GHG emissions with sufficient accuracy and spatial resolution sufficient to independently verify nations' compliance with future treaty limits practical or affordable.